Semiconductor constructions

ABSTRACT

The invention includes methods of forming oxide structures under corners of transistor gate stacks and adjacent trenched isolation regions. Such methods can include exposure of a semiconductor material to steam and H 2 , with the H 2  being present to a concentration of from about 2% to about 40%, by volume. An oxide structure formed under the bottom corner of a transistor gate stack can have a bottom surface with a topography that includes a step of at least about 50 Å, and an upper surface directly over the bottom surface and having a topography that is substantially planar. Methodology of the present invention can be utilized to form semiconductor constructions suitable for incorporation into highly integrated circuitry. The highly integrated circuitry can be incorporated into electronic systems, and can, for example, be utilized in processors and/or memory storage devices.

RELATED PATENT DATA

This patent resulted from a continuation of U.S. patent application Ser.No. 12/276,235, which was filed Nov. 21, 2008, which issued Aug. 24,2010 as U.S. Pat. No. 7,781,860, which is hereby incorporated herein byreference; which resulted from a divisional of U.S. patent applicationSer. No. 11/197,882, which was filed Aug. 5, 2005, which issued as U.S.Pat. No. 7,473,615, and which is hereby incorporated herein byreference.

TECHNICAL FIELD

The invention pertains to semiconductor processing methods,semiconductor constructions, and electronic systems.

BACKGROUND OF THE INVENTION

Trenched isolation regions are commonly utilized for electricallyisolating adjacent structures in highly integrated semiconductorconstructions. A common form of trenched isolation region is a so-calledshallow trench isolation (STI) region.

The trenched isolation regions can be utilized, for example, forproviding isolation between adjacent transistor structures. A difficultywhich can occur when utilizing a trenched isolation region adjacent atransistor structure is that a sharp active corner at the trenchedisolation region edge can lead to a high fringing electric field, whichcan establish a parasitic transistor with a lower threshold voltage(V_(t)) along the trench edge in parallel to the normal transistor. Anedge transistor with a lower V_(t) provides a leakage path even beforethe normal transistor is turned “on.” This can lead to numerous problemsduring operation of the transistor, and can manifest as a “double hump”in the sub-threshold characteristics of the transistor.

Another problem that can occur with field oxide is thinning of the fieldoxide at corners under transistor gates. The thinning can occur due tothermal oxide tending to not grow as thick on the corners as in thecentral region of the field oxide. The thinning of the field oxide atthe corners can exacerbate the fringing electric field problemsdiscussed above, and can lead to decreased reliability of the oxide.

Numerous approaches have been developed for attempting to alleviateproblems associated with sharp active corners at trenched isolationregion edges, but such approaches have not yet proven to be fullysatisfactory. Accordingly, it would be desirable to develop newmethodologies for alleviating problems associated with sharp activecorners at trenched isolation region edges.

SUMMARY OF THE INVENTION

In one aspect, the invention includes a semiconductor processing method.A semiconductor substrate is provided to have a patterned maskthereover. A trench is formed in the substrate proximate the mask. Afterthe trench is formed, the mask is laterally recessed. The substrate isoxidized utilizing an oxidant in the presence of hydrogen to form anoxide structure between the trench and the laterally-recessed mask.Insulative material is deposited within the trench and over the oxidestructure. While at least some of the oxide structure remains, at leasta portion of the mask is replaced with at least a portion of atransistor gate stack.

In one aspect, the invention encompasses a semiconductor processingmethod in which a construction is provided which has upwardly-extendingmesas of semiconductor material, and has nitride-containing structureson the mesas. The nitride-containing structures are laterally recessed.The semiconductor material is oxidized utilizing an oxidant in thepresence of hydrogen to form oxide structures on the mesas beside thelaterally-recessed nitride-containing structures. Insulative material isdeposited over the oxide structures. While at least portions of theoxide structures are on the mesas, at least portions of thenitride-containing structures are replaced with at least portions oftransistor gate stacks.

In one aspect, the invention includes a semiconductor construction. Theconstruction includes a semiconductor substrate having trenchesextending into a semiconductor material, and having regions of thesemiconductor material between the trenches. Individual regions of thesemiconductor material have opposing pairs of lateral edge portionsalong the trenches, and have central portions between the opposing pairsof lateral edge portions. An electrically conductive line extends acrosstwo or more of the regions of the semiconductor material. A dielectricmaterial is between the electrically conductive line and the regions ofthe semiconductor material. At least some of the dielectric materialincludes oxide over the lateral edge portions of the regions, with theoxide having a bottom surface with a topography that includes a step ofat least about 50 Å, and having an upper surface directly over thebottom surface with a topography that is substantially planar.

In one aspect, the invention includes an electronic system. The systemcomprises a processor, and a memory storage device in data communicationwith the processor. At least one of the memory storage device and theprocessor comprises a semiconductor substrate having trenches extendinginto a semiconductor material, and having regions of the semiconductormaterial between the trenches. Individual regions of the semiconductormaterial have opposing pairs of lateral edge portions along the trenchesand have central portions between the opposing pairs of lateral edgeportions. Transistors are associated with at least some of the regionsof the semiconductor material. At least some of the transistors haveelectrically conductive transistor gates over the regions of thesemiconductor material. The transistors also have gate dielectricbetween the transistor gates and the regions of the semiconductormaterial. At least some of the gate dielectric includes oxide over thelateral edge portions of the regions. The oxide has a bottom surfacewith a topography that includes a step of at least about 50 Å, and hasan upper surface directly over the bottom surface and with a topographythat is substantially planar.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic, cross-sectional view of a semiconductor waferfragment at a preliminary processing stage of an exemplary aspect of thepresent invention.

FIG. 2 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 1.

FIG. 3 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 3.

FIG. 5 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 4.

FIG. 6 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 5.

FIG. 7 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 6.

FIG. 8 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 7.

FIG. 9 is a view of the FIG. 1 fragment shown at a processing stagesubsequent to that of FIG. 8.

FIG. 10 is a top view of a portion of a semiconductor wafer comprisingthe fragment of FIG. 9 along the line 9-9.

FIG. 11 is a view along the lines 11-11 of FIGS. 9 and 10, and shows anexemplary transistor device that can be formed along a segment of theconstructions of FIGS. 9 and 10. The fragment of FIG. 9 is along theline 9-9 of FIG. 11.

FIG. 12 is an expanded view of a region labeled “12” in FIG. 5.

FIG. 13 is an expanded view of a region labeled “13” in FIG. 9.

FIG. 14 is a diagrammatic view of a computer illustrating an exemplaryapplication of the present invention.

FIG. 15 is a block diagram showing particular features of themotherboard of the FIG. 14 computer.

FIG. 16 is a high-level block diagram of an electronic system accordingto an exemplary aspect of the present invention.

FIG. 17 is a simplified block diagram of an exemplary memory deviceaccording to an aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

In some aspects, the invention includes methods of forming a desirableprofile at a field edge active area. In particular aspects, such profileis created by recessing a nitride-containing masking material to exposean underlying silicon-containing material, and subsequently oxidizingthe silicon-containing material with steam having H₂ present therein toa concentration of from about 2% to about 40%, by volume. The desiredprofile can be within an oxide structure formed under the bottom cornerof a transistor gate stack. Such oxide structure can have a bottomsurface with a topography that includes a step of at least about 50 Å,and can have an upper surface directly over the bottom surface and witha topography that is substantially planar.

An exemplary aspect of the invention is described with reference toFIGS. 1-13.

Referring to FIG. 1, a fragment 10 of a semiconductor wafer constructionis illustrated at a preliminary processing stage. Fragment 10 comprisesa semiconductor substrate 12. Such substrate can comprise anysemiconductor material or combination of semiconductor materials. Inparticular aspects, the substrate will comprise, consist essentially of,or consist of monocrystalline silicon of a bulk silicon wafer. Suchmonocrystalline silicon can be lightly background doped with p-typedopant. To aid in interpretation of the claims that follow, the terms“semiconductive substrate” and “semiconductor substrate” are defined tomean any construction comprising semiconductive material, including, butnot limited to, bulk semiconductive materials such as a semiconductivewafer (either alone or in assemblies comprising other materialsthereon), and semiconductive material layers (either alone or inassemblies comprising other materials). The term “substrate” refers toany supporting structure, including, but not limited to, thesemiconductive substrates described above.

An oxide-containing layer 14 is over substrate 12. The oxide-containinglayer can, for example, comprise, consist essentially of, or consist ofsilicon dioxide.

A nitride-containing layer 16 is over oxide-containing layer 14.Nitride-containing layer 16 can, for example, comprise, consistessentially of, or consist of silicon nitride.

An oxide-containing layer 18 is over nitride-containing layer 16. Inparticular aspects, oxide-containing layer 14 can be referred to as afirst oxide-containing layer and oxide-containing layer 18 can bereferred to as a second oxide-containing layer. The oxide-containinglayer 18 can comprise, consist essentially of, or consist of silicondioxide, and can be formed by, for example, chemical vapor depositionutilizing tetraethylorthosilicate (TEOS).

Patterned photoresist 20 is over oxide-containing layer 18. Photoresist20 can be patterned by, for example, photolithographic processing. Inthe shown cross-sectional view, the patterned photoresist forms a pairof segments 22 and 24, and defines openings 26, 28 and 30 adjacent thesegments.

Referring to FIG. 2, a pattern is transferred from the patternedphotoresist 20 through the layers 14, 16 and 18, and into substrate 12.Thus, openings 26, 28 and 30 are extended through layers 14, 16 and 18,and into the substrate 12. Such extension of the openings can beaccomplished with any suitable etch, or combination of etches.

The openings 26, 28 and 30 of FIG. 2 can, in particular aspects,correspond to trenches extending longitudinally into and out of the pagerelative to the cross-sectional view of FIG. 2.

The substrate 12 can be considered to comprise upwardly-extendingportions 32 and 34 beneath the segments 22 and 24 of the patternedresist 20. Such upwardly-extending portions of the substrate canalternatively be referred to as upwardly-extending mesas of thesubstrate provided between openings 26, 28 and 30.

Although the patterned photoresist 20 is shown remaining over substrate12 after extension of openings 26, 28 and 30 into the substrate, it isto be understood that the invention also encompasses aspects in which apattern from resist 20 is transferred to one or more of the underlyinglayers 14, 16 and 18, and then resist 20 is removed and the patternedunderlying layers are utilized as a hard mask during subsequent etchingto extend the openings 26, 28 and 30 beyond the patterned layers.Regardless of whether any of the layers 14, 16, 18 and 20 is removedprior to extending the openings 26, 28 and 30 into substrate 12, each ofthe layers remaining at the processing stage of FIG. 2 can be consideredto be a patterned mask remaining over the upwardly-extending mesas 32and 34 of the substrate. Also, any combination or sub-combination of thelayers remaining over the mesas 32 and 34 at the processing stage ofFIG. 2 can be considered to be a patterned mask. In particular aspectsin which nitride-containing layer 16 remains over the mesas 32 and 34,the patterned structures over such layers can be referred to as anitride-containing mask. For instance, the combination of layers 14 and16 can be considered to be a nitride-containing mask.

The stacks of layers 14, 16 and 18 under segments 22 and 24 containsubstantially vertical sidewalls 31 and 33, respectively; and suchsidewalls are coextensive with substantially vertical sidewalls 35 and37, respectively, of mesas 32 and 34.

Referring to FIG. 3, nitride-containing material of layer 16 islaterally recessed to reduce the lateral widths of thenitride-containing structures (or segments) comprised of the layer 16.Layer 16 can be laterally recessed by, for example, from about 50 Å toabout 200 Å per side, and will typically be laterally recessed by about100 Å per side.

The lateral recessing can be accomplished with any suitable etch of thenitride-containing material, and preferably with an etch which isselective for the nitride-containing material of layer 16 relative toother exposed materials of construction 10. In other words, the layer 16is preferably removed with an etch which removes the nitride-containingmaterial of layer 16 faster than other exposed materials of substrate10, which can include, but which is not limited to, etches which are100% selective for layer 16 relative to other exposed materials ofconstruction 10.

The etch can be an isotropic dry etch in some exemplary aspects, and inother exemplary aspects can be a wet nitride strip. For instance, theetch can be a dry nitride strip using H₂, N₂, CF₄ and O₂. In aparticular aspect, the etch can use a flow of the following: N₂ with3.8% H₂ at 700 standard cubic centimeters per minute (sccm) to 1600sccm; CF₄ at 30 sccm to 200 sccm; and O₂ at 40 sccm to 1000 sccm. Apressure during such etch can be from about 0.5 torr to about 2.5 torr;a temperature can be from about 20° C. to about 120° C.; and a microwavepower can be from about 500 watts to about 3000 watts. Other gases canbe used in addition to, or alternatively to, one or more of the H₂, N₂,CF₄ and O₂. Such other gases can comprise, for example, N₂O and H₂; H₂Oand N₂; CHF₃; and NF₃.

As another example, the etch can be a wet nitride strip utilizing hotphosphoric acid for a time of from about 90 seconds to about 480 seconds(with the hot phosphoric acid stripping the nitride at a rate of about44 Å per minute, and accordingly removing from about 60 Å to about 350 Åof the exposed nitride-containing material of layer 16).

In the shown aspect of the invention, photoresist 20 remains overconstruction 10 during the nitride strip. The photoresist can protectregions associated with the semiconductor wafer 12 which are peripheralto the fragment 10 of FIG. 3, and which can have damage induced thereinby the conditions utilized for the nitride strip. The invention canalso, however, include aspects in which the photoresist 20 is removedprior to the nitride strip. Regardless, the materials overnitride-containing layer 16 protect an upper surface of such layerduring the isotropic conditions utilized for laterally recessingsidewalls of the layer.

The lateral recessing of the sidewalls of layer 16 exposes portions 40,42, 44 and 46 of oxide-containing layer 14. The portion 40 is over mesa32, and between trench 26 and a laterally-recessed sidewall of layer 16;the portion 42 is over mesa 32 and between trench 28 and alaterally-recessed sidewall of layer 16; the portion 44 is over a mesa34 and between trench 28 and a laterally-recessed sidewall of layer 16;and the portion 46 is over mesa 34 and between trench 30 and alaterally-recessed portion of layer 16.

Referring to FIG. 4, portions 40, 42, 44 and 46 (FIG. 3) ofoxide-containing layer 14 are removed to expose regions 50, 52, 54 and56, respectively of the semiconductor material of substrate 12 of mesas32 and 34. As discussed previously, such semiconductor material can, inparticular aspects, comprise, consist essentially of, or consist ofsilicon.

The shown removal of portions of oxide-containing layer 14 has extendedto under nitride-containing material 16 to form recesses 60, 62, 64 and66.

The removal of exposed portions of oxide-containing layer 14 can beaccomplished with any suitable etch, and in particular aspects isaccomplished with a buffered oxide etch such as, for example, an etchusing a ratio of about 20:1 of H₂O:HF, under room temperatureconditions.

In the shown aspect of the invention, layers 18 and 20 are removed fromover layer 16 prior to the processing stage of FIG. 4. Such removal canoccur before, during or after the oxide etch utilized to remove exposedportions of oxide-containing layer 14. For instance, photoresist 20 canfirst be removed, and then layers 18 and 14 can both be exposed to theoxide etch utilized to remove exposed portions of layer 14. Such etchcan remove an entirety of oxide-containing layer 18, provided that theetching conditions are conducted for a suitable period of time to removethe thickness of layer 18.

In some aspects of the invention, layers 14 and 16 are togetherconsidered to be a nitride-containing mask. In such aspects, lateralrecessing of the mask can be considered to comprise both of therecessing of the nitride-containing layer 16 discussed with reference toFIG. 3, and the removal of oxide-containing layer 14 discussed withreference to FIG. 4. Specifically, the lateral recessing of the mask14/16 can be considered to comprise a first step which laterallyrecesses layer 16, and a subsequent step which laterally recessesoxide-containing layer 14.

Referring to FIG. 5, construction 10 is exposed to oxidizing conditionswhich form an oxide-containing material 70 extending within trenches 26,28 and 30, and in the shown aspect of the invention also formsoxide-containing material 70 to extend along exposed surfaces ofnitride-containing layer 16.

The oxidizing utilized to form material 70 consumes semiconductormaterial of substrate 12. A dashed line 71 is provided to show thelocation of the surface of substrate 12 prior to the oxidation (with thedashed line 71 corresponding to the location of the substrate at theprocessing stage of FIG. 4).

In particular aspects, substrate 12 will comprise, consist essentiallyof, or consist of silicon; and accordingly oxide-containing material 70will comprise, consist essentially of, or consist of silicon dioxide inlocations where the oxide is formed by consuming portions of thesubstrate 12. The material 70 is thus shown to merge with theoxide-containing layer 14, which, as discussed above, can also comprise,consist essentially of, or consist of silicon dioxide. The material 70will have a different composition where the material is formed byoxidation of a surface of nitride-containing layer 16. For instance, thematerial 70 can comprise, consist essentially of, or consist of siliconoxynitride in locations where the material 70 is formed by oxidation ofsurfaces of nitride-containing layer 16.

The conditions utilized to form material 70 can be wet thermaloxidation. The oxidation preferably utilizes oxidant in the presence ofhydrogen, and can, for example, comprise in situ steam generation(ISSG). In particular aspects, the oxidation utilizes steam in thepresence of H₂, with the H₂ being present in the steam to aconcentration of from about 2% to about 40%, by volume. In an exemplaryapplication, the steam/H₂ mixture will comprise 33% H₂, by volume, andwill be utilized at a temperature of 1050° C. and a pressure of 12 torrto form oxide-containing material 70 to have a thickness of from about80 Å to about 280 Å along the silicon-containing surfaces of substrate12. A typical thickness of the material 70 along the silicon-containingsurfaces is about 180 Å.

Although the hydrogen is described as being provided as H₂, it is to beunderstood that the steam itself can also be a source of hydrogen, andaccordingly in some cases the hydrogen present in the oxidant can behydrogen of the H₂O of the steam.

An advantage of utilizing hydrogen with the oxidant when formingmaterial 70 is that the material can have different chemical and/orphysical properties than other similar materials formed with differentmethods. For instance, if material 70 consists essentially of, orconsists of silicon dioxide, the material can have different propertiesthan material 14—even if material 14 also consists essentially of, orconsists of silicon dioxide—due to material 70 being formed withdifferent oxidizing conditions than those utilized to form material 14.The differences between the materials 14 and 70 can be, for example,differences in densities of the materials. The differences betweenmaterials 14 and 70 can enable material 14 to be removed somewhatselectively relative to material 70.

The upwardly-projecting portions, or mesas, 32 and 34 of FIG. 5 can beconsidered to be regions of semiconductor material 12 between trenches26, 28 and 30. The region 32 can be considered to comprise an opposingpair of lateral edge portions 80 and 82 which are separated from oneanother by a central portion 84 between them. A pair of dashed lines 81and 83 are provided to diagrammatically illustrate approximateboundaries between the lateral edge portion 80 and the central portion84, and between the central portion 84 and the lateral edge portion 82.Region 34 similarly can be considered to comprise a pair of opposinglateral edge portions 90 and 92 separated from one another by a centralportion 94; with dashed lines 91 and 93 being provided todiagrammatically illustrate boundaries between the lateral edge portionsand the central portion.

The material 16 can, in some aspects, be considered to be a firstmaterial in the construction of FIG. 5, and the segments of material 16over regions 32 and 34 can thus be considered to be first materialsegments 100 and 102. The segments 100 and 102 have lateral edges 103and 105, respectively. Also, regions 32 and 34 have lateral edges 107and 109, respectively. The lateral edges 103 of segment 100 arelaterally inset relative to the edges 107 of the underlyingupwardly-extending region 32 of the semiconductor material, andsimilarly the lateral edges 105 are laterally inset relative to thelateral edges 109 of upwardly-projecting region 34 of the semiconductormaterial.

The oxide material 70 forms a pair of oxide structures 110 and 112 overprojection 32 and specifically across the lateral edge portions 80 and82 of such projection. Similarly, the oxide material 70 forms a pair ofoxide structures 114 and 116 across projection 34, and specificallyacross the lateral edge portions 90 and 92 of such projection.

FIG. 12 shows an expanded region of the FIG. 5 structure, andillustrates that oxide-containing structure 110 comprises a bottomsurface 121, and similarly oxide-containing structure 112 comprises abottom surface 123. The oxide-containing structures 110 and 112 alsocontain top surfaces 141 and 143, respectively. In particular aspects,the oxide-containing material 70 consists essentially of, or consists ofsilicon dioxide along projection 32, and then changes composition toconsist essentially of, or consist of silicon oxynitride alongnitride-containing material 16. In such aspects, the upper surfaces 141and 143 comprise regions along projection 32 which consist essentiallyof, or consist of silicon dioxide; and also comprise regions alongmaterial 16 which consist essentially of, or consist of siliconoxynitride.

The top surfaces have topographies which are substantially horizontal.In contrast, the bottom surfaces have topographies which include steps.Specifically, the surface 121 has a topography which includes a step125, and the surface 123 has a topography which includes a step 127. Thesteps extend upwardly from substantially horizontal portions 129 and 131of the bottom surfaces. In particular aspects, the steps can extendapproximately perpendicularly to the substantially horizontal portionsof the bottom surfaces (i.e., can be within about 10 degrees ofperpendicular to the bottom surfaces), and in other aspects the stepscan extend in directions which are not approximately perpendicular tothe substantially horizontal portions of the bottom surfaces. Forinstance, the steps can extend at approximately a 45 degree angle to thehorizontal portions in some aspects of the invention.

The step 125 extends across an elevational distance between thehorizontal surface portion 129 and a substantially horizontal uppersurface 133 of the mesa 32. Such elevational distance is typically fromat least about 50 Å to less than or equal to about 150 Å. The step 127,similarly to the step 125, extends across the elevational distancebetween the horizontal surface portion 131 and the upper surface 133 ofthe mesa 32.

The steps 125 and 127 can be in the form of single steps (as shown), orcan comprise multiple small steps which together span the elevationaldistance from the substantially horizontal bottom surfaces 129 and 131to the surface 133 atop projection 32.

In the shown aspect of the invention, a portion of the oxide-containinglayer 14 remains under the segment of material 16, and the oxide 70merges with the oxide-containing layer 14. The steps 125 and 127 occurat approximate locations where the merger of material 70 and material 14occurs. Thus, the length of layer 14 at the processing stage of FIG. 4dictates the distance between the steps 125 and 127. Steps 125 and 127can occur at any suitable location relative to outer lateral surfaces107 of projection 32. The steps are approximately shown distances 150and 152 from surfaces 107. In particular aspects, such distances can befrom at least about 100 Å to less than or equal to about 300 Å. In someaspects, the distances 150 and 152 can be at least about 100 Å. Also,although distances 150 and 152 are shown to be about the same as oneanother, it is to be understood that the invention can also encompassaspects in which distances 150 and 152 are different from one another.

Referring to FIG. 6, electrically insulative material 160 is depositedwithin trenches 26, 28 and 30, and over oxide structures 110, 112, 114and 116. The insulative material 160 is ultimately incorporated intotrenched isolation structures in typical aspects of the invention.Accordingly, the material 160 can comprise any material suitable forincorporation into trenched isolation structures, including, forexample, silicon dioxide formed utilizing a high density plasma(so-called HDP oxide).

A substantially planar uppermost surface 161 is shown extending acrossmaterial 160 and segments 100 and 102 of material 16. Such substantiallyplanar surface can be formed by, for example, chemical-mechanicalpolishing after deposition of insulative material 160.

Referring to FIG. 7, nitride-containing layer 16 is removed utilizing anappropriate etch. Such etch can comprise, for example, an isotropic dryetch, or a wet nitride etch, such as, for example, one of the etchesdiscussed above for laterally recessing the material 16 at theprocessing stage of FIG. 3. The removal of material 16 forms openings162 and 164 which expose portions of oxide-containing structures 110,112, 114 and 116; and which also exposes remaining portions ofoxide-containing layer 14.

Referring to FIG. 8, an oxide etch is utilized to remove oxide 14 fromover upper surfaces 133 of upwardly-projecting regions 32 and 34. Theetch selectively removes oxide-containing material 14 relative to theoxide material 70. Such selectivity can occur even though materials 14and 70 have the same composition as one another. Numerous possiblemechanisms exist for how oxide material 14 can be selectively removedrelative to oxide 70. Some of the mechanisms will be specificallydescribed herein. Such mechanisms are provided to assist the reader inunderstanding the invention. The invention is not, however, to belimited to such mechanisms except to the extent, if any, that suchmechanisms are expressly recited in the claims that follow.

Exemplary mechanisms by which etch selectivity for an oxide material 14relative to an oxide material 70 having the same composition as material14 can occur are if the materials have different physical propertiesrelative to one another, such as differences in density, for example;and/or if geometric constraints make it more difficult to remove oxidematerial 70 than oxide material 14 (for instance, surface tensioneffects may render it difficult for an oxide etch to attack recessedcorners associated with oxide 70).

In particular aspects of the invention, oxide 14 will consist of silicondioxide formed by thermal oxidation of silicon-containing material ofsubstrate 12 in the absence of hydrogen, and oxide 70 will consist ofsilicon dioxide formed by oxidation of silicon-containing materialsubstrate 12 in the presence of hydrogen. Such difference inmethodologies for formation of oxide 70 relative to oxide 14 can lead tophysical differences between the silicon dioxide of material 70 relativeto the silicon dioxide of material 14 so that material 14 can beselectively removed relative to material 70. The “selective removal” ofoxide 14 means that oxide 14 is removed faster than oxide 70, which caninclude, but is not limited to, aspects in which the selectivity is 100%for oxide 14 relative to the oxide 70. It is noted, however that some ofoxide 70 is removed by the etch of oxide 14. Specifically theprojections of oxide 70 that had been along nitride layer 16, and hencecomprised silicon oxynitride rather than silicon dioxide, are present atthe processing stage of FIG. 7, and removed by the etch utilized to formthe construction of FIG. 8.

The selective removal of oxide 14 can be accomplished with, for example,a buffered oxide etch of the type described previously for recessing theoxide 14 to form the structure of FIG. 4.

In the shown aspect of the invention, the removal of oxide 14 isaccompanied by dishing into material 160 to widen openings 162, andaccordingly the openings 162 are wider at the processing stage of FIG. 8than at the processing stage of FIG. 7.

Referring to FIG. 9, gate dielectric material 170 is provided atopsemiconductor material projections 32 and 34. The gate dielectricmaterial can, for example, comprise, consist essentially of, or consistof silicon dioxide. Such can be formed by, for example, thermaloxidation of the semiconductor material of projections 32 and 34.

Electrically conductive gate material 172 is provided over the gatedielectric 170 as a line extending across both of regions 32 and 34, andwithin openings 162 and 164. The electrically conductive gate materialcan comprise any suitable composition or combination of compositions,and in particular aspects will comprise, consist essentially of, orconsist of one or more of conductively-doped semiconductor material(such as, for example, conductively-doped silicon), metal (such as, forexample, titanium or tungsten), and metal compounds (such as, forexample, titanium silicide).

An electrically insulative protective material 174 is formed over line172. Material 174 can comprise any suitable composition or combinationof compositions, and in particular aspects will comprise one or more ofsilicon dioxide, silicon nitride and silicon oxynitride.

The line 172 can be a wordline utilized to form transistor constructionsof a memory array, as described with reference to FIGS. 10 and 11.

FIG. 10 shows a top view of a portion of a wafer comprising the fragmentof FIG. 9, and shows that the isolation regions 160 can extend alongopposing sides of the line shown in FIG. 9. FIG. 10 also shows thatsource/drain regions 180 and 182 can extend in and out of the pagerelative to the projection 32 of the cross-section of FIG. 9; andsimilarly source/drain regions 184 and 186 can extend in and out of thepage relative to the projection 34 of the cross-sectional view of FIG.9. Each of the regions where the line 174 crosses between pairedsource/drain regions can be considered to correspond to a transistordevice, with one of the transistor devices of FIG. 10 being labeled as190, and the other being labeled as 192. Such transistor devices havefield edges 191 and 193, respectively. The field edges are also shown inFIG. 9, and correspond approximately to the outermost lateral edges ofprojections 34 and 36.

The cross-section of FIG. 11 shows transistor device 190, andspecifically shows that the dielectric material 170, conductive gatematerial 172 and protective insulative material 174 can be togetherincorporated into a transistor gate stack. The gate stack contains atransistor gate which couples source/drain regions 182 and 180 with oneanother. The region of substrate 12 under dielectric material 170 can bedoped with a threshold voltage (V_(T)) implant, as such region is achannel region between the source/drain regions.

A pair of sidewall spacers 194 are shown along sidewall edges of thegate stack, as would be a typical construction. The sidewall spacers cancomprise, for example, one or more of silicon dioxide, silicon nitride,and silicon oxynitride.

The transistor device 190 can be incorporated into any of numerousintegrated circuit constructions. The source/drain region 180 is showncoupled to circuitry 200, and the source/drain region 182 is showncoupled to circuitry 202. The transistor device 190 can be utilized as alogic device if it is coupled to appropriate circuitry 200 and 202, orcan be incorporated into a memory unit cell if it is coupled with othercircuitry 200 and 202. For instance, the transistor device 190 can beincorporated into a dynamic random access memory (DRAM) unit cell if oneof the circuit devices 200 or 202 is a charge-storage device (such as,for example, a capacitor), and the other is an electrical connection toa bitline. A plurality of such DRAM unit cells can be togetherincorporated into a memory array.

The formation of one or more of the gate stack layers 170, 172 and 174of FIG. 9 within locations vacated by one or both of masking materials14 and 16 can be considered replacement of at least a portion of a maskwith at least a portion of a transistor gate stack.

FIG. 13 shows an expanded view of a region 13 of the FIG. 9cross-section. FIG. 13 shows that semiconductor material region 34comprises the opposing pair of lateral edge portions 80 and 82 describedwith reference to FIG. 12, and comprises the central portion 84 betweenthe lateral edge portions. The construction of FIG. 13 also comprisesthe oxide structures 110 and 112 formed of oxide-containing material 70.Such structures contain the bottom surfaces 121 and 123 having thetopography comprising substantially horizontal portions 129 and 131, andsteps 125. Further, the oxide structures 110 and 112 have upper surfaces250 and 252, respectively, which are directly over the bottom surfaces121 and 123. Such upper surfaces 250 and 252 are substantially planar,and are much more planar than the bottom surfaces comprising the steps125 and 127. In particular aspects, the upper surfaces will be planar towithin 10 Å, and in some aspects will be planar to within 5 Å, inlocations where the upper surfaces are extending directly over both thesubstantially horizontal portions (129 and 131) and step portions (125and 127) of the bottom surfaces.

In some aspects, materials 70, 160 and 170 all consist essentially of orconsist of silicon dioxide. In such aspects, the materials can beconsidered to merge to form a single oxide. The single oxide hasuppermost surfaces 257 and 259 over bottom surfaces 121 and 123. Theuppermost surfaces 257 and 259 are substantially planar, and are muchmore planar than the bottom surfaces comprising the steps 125 and 127.In particular aspects, the upper surfaces 257 and 259 will be planar towithin 10 Å, and in some aspects will be planar to within 5 Å, inlocations where such upper surfaces are extending directly over both thesubstantially horizontal portions (129 and 131) and step portions (125and 127) of the bottom surfaces.

The construction of FIG. 13 advantageously has recessed corners 253 and255 beneath the gate transistor device 190 adjacent the isolation oxide160. Such recessed corners correspond to regions within the oxidestructures 110 and 112 where the steps 125 and 127 join with thesubstantially horizontal portions 129 and 131. The recessed corners 253and 255 can alleviate detrimental fringing electric fields of the typediscussed in the “Background” section of this disclosure.

The construction of FIG. 13 can also avoid the problem of thinning ofthe field oxide that was discussed in the “Background” section of thisdisclosure. Regardless of whether there is a sharp corner on the lowersurfaces 121 and 123, the thickness of the oxide between such lowersurfaces and the gate material 172 can mitigate fringing-field-relatedissues that would otherwise be associated with the corners if the oxidewere thinner at the corners.

In some aspects, the structure of FIG. 13 can be considered to havesteps near the field edges of the semiconductor material of projection32. Yet, the gate of transistor device 190 (specifically, the conductivematerial 172) does not follow the contour of the silicon substrate.Rather it follows a horizontal or nearly horizontal contour along anupper surfaces of the oxides 70 and 170. Such can be advantageous formaintaining desired uniformity across numerous transistor gates, and formaintaining desired properties of individual gates.

The invention can have numerous advantages relative to various methodsthat have been attempted in the prior art to alleviate fringing affects.Such advantages can include: (1) The invention can be simple toimplement, (2) the invention can be inexpensive to implement, (3) theinvention can be robust to process variation, and (4) the invention canprovide a relatively large margin to thinning.

Devices formed in accordance with aspects of the present invention canbe utilized in numerous electronic systems. FIGS. 14-17 describeexemplary electronic systems.

FIG. 14 illustrates generally, by way of example but not by way oflimitation, an embodiment of a computer system 400 according to anaspect of the present invention. Computer system 400 includes a monitor401 or other communication output device, a keyboard 402 or othercommunication input device, and a motherboard 404. Motherboard 404 cancarry a microprocessor 406 or other data processing unit, and at leastone memory device 408. Memory device 408 can comprise various aspects ofthe invention described above. Memory device 408 can comprise an arrayof memory cells, and such array can be coupled with addressing circuitryfor accessing individual memory cells in the array. Further, the memorycell array can be coupled to a read circuit for reading data from thememory cells. The addressing and read circuitry can be utilized forconveying information between memory device 408 and processor 406. Suchis illustrated in the block diagram of the motherboard 404 shown in FIG.15. In such block diagram, the addressing circuitry is illustrated as410 and the read circuitry is illustrated as 412. Various components ofcomputer system 400, including processor 406, can comprise one or moreof the memory constructions described previously in this disclosure.

Processor device 406 can correspond to a processor module, andassociated memory utilized with the module can comprise teachings of thepresent invention.

Memory device 408 can correspond to a memory module. For example, singlein-line memory modules (SIMMs) and dual in-line memory modules (DIMMs)may be used in the implementation which utilize the teachings of thepresent invention. The memory device can be incorporated into any of avariety of designs which provide different methods of reading from andwriting to memory cells of the device. One such method is the page modeoperation. Page mode operations in a DRAM are defined by the method ofaccessing a row of a memory cell arrays and randomly accessing differentcolumns of the array. Data stored at the row and column intersection canbe read and output while that column is accessed.

An alternate type of device is the extended data output (EDO) memorywhich allows data stored at a memory array address to be available asoutput after the addressed column has been closed. This memory canincrease some communication speeds by allowing shorter access signalswithout reducing the time in which memory output data is available on amemory bus. Other alternative types of devices include SDRAM, DDR SDRAM,SLDRAM, VRAM and Direct RDRAM, as well as others such as SRAM or Flashmemories.

Memory device 408 can comprise memory formed in accordance with one ormore aspects of the present invention.

FIG. 16 illustrates a simplified block diagram of a high-levelorganization of various embodiments of an exemplary electronic system700 of the present invention. System 700 can correspond to, for example,a computer system, a process control system, or any other system thatemploys a processor and associated memory. Electronic system 700 hasfunctional elements, including a processor or arithmetic/logic unit(ALU) 702, a control unit 704, a memory device unit 706 and aninput/output (I/O) device 708. Generally, electronic system 700 willhave a native set of instructions that specify operations to beperformed on data by the processor 702 and other interactions betweenthe processor 702, the memory device unit 706 and the I/O devices 708.The control unit 704 coordinates all operations of the processor 702,the memory device 706 and the I/O devices 708 by continuously cyclingthrough a set of operations that cause instructions to be fetched fromthe memory device 706 and executed. In various embodiments, the memorydevice 706 includes, but is not limited to, random access memory (RAM)devices, read-only memory (ROM) devices, and peripheral devices such asa floppy disk drive and a compact disk CD-ROM drive. One of ordinaryskill in the art will understand, upon reading and comprehending thisdisclosure, that any of the illustrated electrical components arecapable of being fabricated to include memory constructions inaccordance with various aspects of the present invention.

FIG. 17 is a simplified block diagram of a high-level organization ofvarious embodiments of an exemplary electronic system 800. The system800 includes a memory device 802 that has an array of memory cells 804,address decoder 806, row access circuitry 808, column access circuitry810, read/write control circuitry 812 for controlling operations, andinput/output circuitry 814. The memory device 802 further includes powercircuitry 816, and sensors 820, such as current sensors for determiningwhether a memory cell is in a low-threshold conducting state or in ahigh-threshold non-conducting state. The illustrated power circuitry 816includes power supply circuitry 880, circuitry 882 for providing areference voltage, circuitry 884 for providing the first wordline withpulses, circuitry 886 for providing the second wordline with pulses, andcircuitry 888 for providing the bitline with pulses. The system 800 alsoincludes a processor 822, or memory controller for memory accessing.

The memory device 802 receives control signals from the processor 822over wiring or metallization lines. The memory device 802 is used tostore data which is accessed via I/O lines. It will be appreciated bythose skilled in the art that additional circuitry and control signalscan be provided, and that the memory device 802 has been simplified tohelp focus on the invention. At least one of the processor 822 or memorydevice 802 can include a memory construction of the type describedpreviously in this disclosure.

The various illustrated systems of this disclosure are intended toprovide a general understanding of various applications for thecircuitry and structures of the present invention, and are not intendedto serve as a complete description of all the elements and features ofan electronic system using memory cells in accordance with aspects ofthe present invention. One of the ordinary skill in the art willunderstand that the various electronic systems can be fabricated insingle-package processing units, or even on a single semiconductor chip,in order to reduce the communication time between the processor and thememory device(s).

Applications for memory cells can include electronic systems for use inmemory modules, device drivers, power modules, communication modems,processor modules, and application-specific modules, and may includemultilayer, multichip modules. Such circuitry can further be asubcomponent of a variety of electronic systems, such as a clock, atelevision, a cell phone, a personal computer, an automobile, anindustrial control system, an aircraft, and others.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A semiconductor construction, comprising: a region of semiconductormaterial having a central portion between a pair of lateral edgeportions; an electrically conductive line over the region of thesemiconductor material; a dielectric material between the electricallyconductive line and the region of the semiconductor material; thedielectric material having a bottom surface with a topography thatincludes a step of at least about 50 Å, and an upper surface directlyover the bottom surface and having a topography that is substantiallyplanar; and wherein the line has a thick segment over the region of thesemiconductor material and a thin segment adjacent the thick segment. 2.The construction of claim 1 wherein said step is from at least about 50Å to less than or equal to about 150 Å.
 3. The construction of claim 1wherein the bottom surface comprises a substantially horizontal portionadjacent the step, and wherein the step is approximately perpendicularto said substantially horizontal portion.
 4. The construction of claim 1wherein the bottom surface comprises a substantially horizontal portionadjacent the step, and wherein the step is not approximatelyperpendicular to said substantially horizontal portion.
 5. Theconstruction of claim 1 wherein the dielectric material consists ofsilicon dioxide.
 6. A semiconductor construction, comprising: asemiconductor substrate having trenches extending into monocrystallinesilicon, and having pedestals of the monocrystalline silicon between thetrenches; individual pedestals having opposing pairs of lateral edgeportions along the trenches and central portions between the opposingpairs of lateral edge portions; an electrically conductive structureextending across two or more of the pedestals; and a dielectric materialbetween the electrically conductive structure and the pedestals; thedielectric material including oxide over the lateral edge portions ofthe pedestals, the oxide having a bottom surface with a topography thatincludes a step of at least about 50 Å, and an upper surface directlyover the bottom surface and having a topography that is substantiallyplanar.
 7. The construction of claim 6 further comprising electricallyinsulative isolation structures within the trenches and between thepedestals, and wherein the electrically conductive structure extendsacross two or more of the isolation structures.
 8. The construction ofclaim 6 wherein the oxide consists of silicon dioxide.
 9. Asemiconductor construction, comprising: a monocrystalline siliconsubstrate having trenches extending therein; regions of themonocrystalline silicon being between the trenches; individual regionsof the monocrystalline silicon having opposing pairs of lateral edgeportions along the trenches and central portions between the opposingpairs of lateral edge portions; an electrically conductive lineextending across two or more of the regions of the monocrystallinesilicon; a dielectric material between the electrically conductive lineand the regions of the monocrystalline silicon; the dielectric materialincluding oxide over the lateral edge portions of the regions, the oxidehaving a bottom surface with a topography that includes a step of atleast about 50 Å, and an upper surface directly over the bottom surfaceand having a topography that is substantially planar; and wherein theline has thick segments over the regions of the monocrystalline siliconand thin segments between the thick segments.